Главная страница | назад





Article #17146: Creating a Lookup field at runtime

 Question and Answer Database

FAQ2146D.txt   Creating a Lookup field at runtime
Category   :Database/VCL
Platform    :All
Product    :All 32 bit  

Question:
How can I create a lookup field at runtime?

Answer:
Creating a lookup field at runtime differs in only a few ways from
creating any standard TField object.  Three properties of a field
that must be set in order to function as a Lookup field are 
LookUpDataset, LookUpKeyFields and LookUpResultField.  The sample 
code below demonstrates how to create a Lookup field at runtime 
using the two DBDEMOS tables 'customer.DB' and 'orders.DB'.
 
Example:

uses
  Forms, Classes, Controls, StdCtrls, Db, DBTables, DBCtrls;


type
  TForm1 = class(TForm)
    Table1: TTable;   // DBDemos customer table
    Table2: TTable;   // DBDemos orders table
    Button1: TButton;
    DBLookupComboBox1: TDBLookupComboBox;
    DataSource1: TDataSource;
    Table2CustNo: TFloatField;  // CustNo key field object used for Lookup  
    procedure Button1Click(Sender: TObject);
  private
    { Private declarations }
  public
    { Public declarations }
  end;

var
  Form1: TForm1;

implementation

{$R *.DFM}

procedure TForm1.Button1Click(Sender: TObject);
begin
  with TStringField.Create(Table2) do begin
    FieldName := 'MyLookup';
    FieldKind:= fkLookup;
    DataSet := Table2;  
    Name := Dataset.Name + FieldName;
    KeyFields:= 'CustNo';
    LookUpDataset:= Table1;
    LookUpKeyFields:= 'CustNo';
    LookUpResultField:= 'Company';
    DbLookupCombobox1.DataField:= FieldName;
    DataSource1.DataSet:= Dataset;
    Table2.FieldDefs.Add(Name, ftString, 20, false);
  end;
  DbLookupCombobox1.DataSource:= Datasource1;
  Table1.Active:= True;
  Table2.Active:= True;
end;

end.

7/16/98 4:31:28 PM
 

Last Modified: 01-SEP-99